The present invention relates generally to a pay telephone unit that derives its operating power solely from the telephone line, without a source of external power. More particularly, the invention relates to a line-powered pay telephone unit that does not require a battery to provide power during an on-hook or off-hook condition.
At one time, all pay telephones were essentially "dumb" boxes consisting of a keypad (or rotary dialer in much earlier phones), handset and coin mechanism. All "intelligence" (previously human operators) resided in expensive equipment located in the telephone company's Central Office (CO). This equipment would sense when a call was being initiated, determine the cost, inform the user of the amount to be deposited, count the deposited coins, determine when a connection had been made, time the call, ask for additional coinage if required, and deposit or refund the coinage as necessary. Disposition of the coinage would depend on whether a valid call resulted or, for example, a busy signal was received or the phone was returned on-hook prior to a connection being established. Operation of the telephone's coin mechanism was controlled from the CO.
With the advent of Customer Owned Coin Operated Telephones (COCOT), all of the functions and decisions that had previously been handled by the CO equipment now had to be accomplished in the phone itself. Advanced electronics made this possible and the "smart phone" came into being. Unlike the common phone found in most homes and businesses, smart phones contain an extensive amount of electronics, essentially a small computer, that needs to be powered.
Until recently, smart phones derived their operating power from conventional AC wiring. The need for AC power, however, has often been a source of significant inconvenience and expense for the owner. The telephone line is supplied to the phone by the telephone company, but AC has to be run separately, often through underground conduit. A licensed electrician is frequently needed for installation of the AC wiring and additional electric metering is sometimes required. In such installations, power may be inadvertently switched off at night or on weekends.
New phones, powered from the telephone line itself, have begun to appear on the market in the last several years. These phones were developed to eliminate the disadvantages of being AC powered. Since only a minuscule amount of power can be drawn from the telephone line in an on-hook condition, rechargeable batteries are often utilized in "line-powered" telephones to supply the additional power required during this time. Depending on the phone's design, battery power may be necessary for data retention, real-time clock operation, and controlling coin and switching relays.
It will be appreciated that the use of batteries gives rise to a number of disadvantages. For example, battery failure or a momentary glitch in power will cause data stored in RAM memory to be erased or corrupted. In addition, the process of battery replacement is often time consuming, costly or otherwise problematic.
One smart phone design powered solely from telephone line power is described in U.S. Pat. No. 5,133,005 to Kelley et al., incorporated herein by reference. This patent teaches that the power provided by the telephone line is not sufficient while on-hook to maintain computer memory or to power-up the phone to initiate calls during alarm conditions. A battery, with its attendant disadvantages, provides the additional power required during the on-hook condition. When the phone is off-hook, the battery is recharged using "excess loop current," i.e., the difference between the current required for use of the phone and the current supplied by the telephone line. In some situations, however, no excess loop current may be available to recharge the battery. It will be appreciated that such a design may encounter operational difficulties if the battery becomes insufficiently charged.